Pulse delay circuit



May 1, 1951 l R. E. MOE 2,551,280

PULSE DELAY CIRCUIT Filed Jan. 29, 1949 2 Sheets-Sheet l PULSE SOURCE 49f TRIGGER Hf,

cmcun' PULSE SOURCE TRIGGER CIRCUIT Inventor: Rbert, EMOe;

bym 0% His Attorney.

May 1951 R. E. MOE

PULSE DELAY CIRCUIT 2 Sheets-Sheet 2 Filed Jan. 29, 1949 Fig.3.

TIME

t, tzt t t t 13 -13 Ihventor: RobePtEMoe, b A) M His Attorney.

Patented May 1, 1951 Robert E. Moe, Syracuse, N. Y, assignor to GeneralElectric Company, a corporation of New York Application January 29,1949, Serial No. 73x41 *Claiiin's. 1

This invention relates generally toelectrical multivibrator circuits andmore particularly to a circuit for accurately determining thetime-duration of a voltage pulse.

An object of this invention is to provide an improved circuit forgenerating a rectangular pulse of voltage having a time-durationaccurately determined as a multiple of the interval between repeatedmarking pulses.

Another object of this invention is to provide a circuit for generatinga rectangular pulse whose time-duration is a sub-multiple of the periodof an applied alternating current wave. 7

A further object of this invention is to provide a stable multivibratorcircuit for generating a square wave upon the occurrence of a voltagepulse and for terminating the duration of said wave at a predeterminedtime after the occurrence of said pulse, said time being determined byan external circuit.

For further objects and advantages and for a better understanding of theinvention, attention is now directed to the followingdesc'ription andaccompanying drawings, and also to the appended claims, in which thefeatures of the invention believed to be novel are more particularlypointed out.

In the drawings, Fig. 1 illustrates schematically a type ofmultivibratorcir'cuit, known iii the art as a cathode-coupledmultivibrator; Fig. '2 illustrates schematically a c'athode coupledmultivibrator with certain improvements embodying my invention; and Fig.3 shows a series ofcurve's illustrating, on a common time scale, voltagevariations and wave forms occurring at various designated points in thecircuit of Figs. 1 and 2.

Referring to Fig. 1, there is shown a source I adapted to supply pulsesof voltage, through a capacitor 2, to the control electrode or grid 3,of an electron discharge device *4, which in conjunction with anotherele'ctrondis'charge device 5, constitutes a multivibrator circuit of thecathode-coupled type. The anodes '6 and I of devices 4 and 5 areconnected through resistances 8 and 9 respectively to a source ofoperating potential indicated by B-+. The cathodes l0 and H 'of bothdevices have a commoncon'nection to ground through a resistor l2. Apotentiometer 13, connected between the source of operating potential 3+and ground, provides, at an adjustable tab 14-, a positive biaspotential for the grid 3"of device 4. The connection from grid 3 to tapit is made through a resistor l'5 which has a sufliciently highresistance to "prevent any substantial dissipatioiiof pulse energy 'ilybe 'thec se To obtains'uchan integral relathe basic "circuit and thepulse source l fope' ted in the potentiometer. The anodeB of device itis coupled to the grid I'G of device {through a capacitor IT, and apositivebias is a ppli 'ed to grid l6 througha resistor lil providing-a'connection to the source of operatingpotentia l l3+r.

A trigger circuit l9 has an input terminal connected to source "and anoutput terj a1 connected to the grid [:6 of device "5. The-f r tion ofthe trigger circuit is to provide, f mediately after the occurre'ncebfapulse the source I, a series of pulsesof predetermined shortertime-duration. Any of the inful'tivibrator circuits known in the art andcapable 'of pro} viding a series of pulses, occurring "at short timeintervals immediately a ftertl ie o'ccurrende of an input pulse whichisrep'eatjed at time intervals, may be used for the purpose. Such acircuit, for instance, is described in the publication Principles ofRadar the B91 r School of the Massachusetts Institutepf ch;-

nology, published by the McGraw- "Company of NEW York in 1946, and again*U. 5. Patent No. 2-,423-,304-Fi c issued July 1,

1947, and entitled fPulse Producing "Syst'e While I have not shown-inthe curves of' any rate era relationship bat-eta the repea rateof t etrigger circuit a d that of the use source, it wiut pparent thatsuchpoulfd tionship, the trigger circuit-l9 could he as therefrom. Withsuch an arrangement, 'p s'e source I may take theformof a counter 51 t,and give for example, one (in ut- 3 1156 01 "every ten pulses suppliedto it from the trigger circuit.

A description of the operation of the electrical multivibrator circuit'otFig. 1 will now segues,

reference being made to 'tl'le curves of Fig, 3.

The inultivibrator circuit 'compri'sing device and 5 is 'oi the typehaving one condition lof stability in which device 4 is normally noonjidu'cting and device 5 is n rm uyeprraueusg. 12 1 i e i p rt o t fa tth .th i'd return of deviceE is made through resistor (8 to the positivesource 13+, whereas the grid retu n oi d evice 4 is made to a sourceegress positive potential, as determined'by the setting of tap M onpotentiometer I3. Also, due to the common cathode eo'nne'ctmn throughresistor 12, the current through aevice 5 "serves to biasthe cathode l0or device 4 in a positive enemies,

thus producing a negative bias on grid 3'o'ft'li'at device, therebyrendering it completely 'ii'o'n conductive.

device 4, a series of pulses occurring at the relatively long timeinterval h to tn, as illustrated by curve 30 of Fig. 3. A positive pulseas grid 3 initiates a first pulse of current through device 4 causing adecrease in voltage at the anode 6, which is coupled back to grid 6 ofdevice 5 as a negative increment of voltage. The negative increment ofvoltage at the grid of device 5 reduces the current through that device,thereby reducing the voltage drop across resistor 2 and furtherincreasing the positive increment of voltage at the grid of device 4,over and above that originally supplied from the source This furtherincrease in the positive increment at the grid of device 4, in turninitiates another similar succession of changes, and thus a switchingprocess occurs which proceeds very rapidly to the point where device 4is conducting very heavily and device 5 has become completelynon-conductive. The voltage at the anode l of device 5 is shown by curve3| of Fig. 3, which illustrates a positive increment of voltageoccurring at a time h, and again at time tn, as determined by theoccurrence of pulses from source A negative increment of voltage, whichis the inverse of the positive increment illustrated in curve 3|, occursat the anode 6 of device 4, and supplies, through coupling capacitor [1,a negative increment of voltage at the grid I6 of device 5. The chargecoupled through capacitor H is dissipated or discharged through resistorH at a rate dependent upon the time-constant of the combination, asillustrated by curve 32 of Fig. 3. In normal course, device 4 remainsconducting, and device 5 non-conducting, until the charge acrosscapacitor I! has decreased to the critical value where conductionthrough device 5 is just on the point of beginning. At that instant, aswitching process in the reverse direction occurs, causing device 4 tobecome non-conducting and device 5 to become conducting. The positiveincrement of voltage at the anode of device 5 is thereby terminated,resulting in the generation of a square pulse of voltage, as illustratedby a curve 3| of Fig. 3.

The time-duration of the square pulse depends vupon the magnitudes ofcapacitor l1 and resistor l8, and also upon the circuit constants of.the associated elements and the operating voltages. The time-duration,as can be appreciated from an inspection of curve 32; is determined bythe intersection of a sloping exponential curve with a certainhorizontal voltage level and, acfcordingly, is not accurately andpositively fixed.

For instance, referring to Fig. 3, curves 3| and :32 representrespectively the anode output voltage, and the control electrode voltageof device 5 for a certain set of operating voltages and circuitconstants. Curves 3|f and 32' represent similar operatingcharacteristics when capacitor l1 and may be anywhere within certainlimits such as tb to to in Fig. 3. Thus, any slight change in supplyvoltages or any drift in circuit constants -due to temperature changesmay shift the actual I time ta of the occurrence of the reverseswitching process.

To provide a more definite fixation or determination of thetime-duration of the rectangular output pulse, it, has been customaryheretofore to apply to the grid of device 5 a sharp pulse which willincrease the voltage on the grid of device 5 to a value sufficient toinitiate the reverse switching process. Thus, the function of thetrigger circuit I9 is to provide a series of trigger pulses occurring atdefinite time intervals after the original input pulse. While the periodbetween trigger pulses is normally an integral sub-multiple of theperiod between pulses from the source there is no necessity that such bethe case, and the trigger pulses may have any desired repetition rate.The output pulses from the circuit l9 are illustrated by curve 33 ofFig. 3. When these pulses are applied to the grid of device 5, they aresuperimposed on the exponential discharge curve and establish definiteinstants in time at which the switching action may occur, as illustratedby curve 34 of Fig. 3. For instance, the switching action would normallyoccur at time t7, and the time-duration of the rectangular output pulseof curve 3| would then be the interval ii to t7, which is equal to 6 ofthe periods of the trigger pulses from the circuit [9.

While the circuit which has been described provides results which areadequate for some applications, the circuit suffers from a considerablemeasure of instability, since it has been found in practice that theswitching action may occur at the instants is to ts, rather than at theinstant 157. This is due to the fact that the timing pulses from thetrigger circuit are superimposed on a gently curving exponential.Accordingly, there is not a great deal of difference in the absolutepotential or voltage to which the grid of device 5 is raised bysuccessive trigger pulses. The result is that the reverse switchingaction definitely occurs at an instant determined by one of the triggerpulses, but the number of the trigger pulse or in other words theparticular individual pulse is not definitely and positively selected.Thus, referring to curve 34, the reverse switching occurs at time t7,but any slight disturbance or variation in circuit constants may make itoccur at times ts or is, and also may cause the switching instant toshift continuously back and forth from one to the other.

My invention resides particularly in an improvement in the circuit forapplying the trigger pulses of curve 33 in a modified form to the gridof device 5, as illustrated in Fig. 2. Referring to Fig.2 in whichcircuit elements performing the same function as in Fig. 1 bear the samenumerals, the grid I6 of device 5 is no longer connected to the sourceof operating potential B+ through a resistor |8, but instead isconnected to ground through a capacitor 2|. The output terminal of thepulsing circuit I9 is now connected to the grid 16 of device 5 in serieswith a resistor 22, a capacitor 23, and a diode 24, which is connectedto conduct current from capacitor 23 to grid l6. Another diode 25 isconnected to conduct current from a point of potential, which isnegative with respect to ground, to the junction of diode 24 andcapacitor 23. The point of negative potential is provided by a tap 26 ona potentiometer 21, of which one terminal is grounded and the otherterminal is connected to a source of negative potential provided by abattery 28. A capacitor 29 connected between ground and tap 26 providesa low impedance path for pulsating currents flowing through diode 25.

When a positive pulse of voltage is supplied to grid 3 of device 4 inthe circuit of Fig. 2, the sequence of events is very similar to thatoccurring in the circuit of Fig. 1. Immediately upon the-occurrence ofthe pulse-at times t1 and 1511, as illustrated in curve 3ll, a switchingaction occurs which renders device 4 conducting and device 5'non-conducting. This 'resultsin a Y positive increment of voltage at theanode of device 5, as illustrated by curve 3!, and also by curve 36, ofFig. 3. Simultaneously, a negative increment of voltage is produced atthe grid 55 of device 5 through the coupling capacitor 9, as illustratedby the negative increment in curve 35 occurring at times t1 and tn.Trigger pulses, as illustrated in curve 33, are applied to the chargingcircuit comprising diode 24, from the trigger circuit i9. These pulsescause small increments of charge to flow through the diode 24, therebyincrementally raising the initial negative potential at'gridlt of device5 toward zero. The voltage at grid 1 6, or in other Words the chargedeveloped across capacitors I? or 2 l, increases in a series of smallincrements or steps, as illustrated by curve 35 of Fig. 3. For eachpulse of voltage supplied from the trigger circuit, an increment ofvoltage appears at grid E6. The size or magnitude of this increment isdependent upon the ratio of the values of capacitors 23 and I? and uponthe ratio of resistance 22 to the anode resistance of device 4. Thefunction of capacitor 2| is simply to stabilize the operation of thecircuit, and its value may be approximately of that of capacitor l1.

The voltage developed across capacitor i! increases in a number ofincrements or steps until it reaches a value sufficient to initiate thereverse switching process and thereby determine the time-duration of theoutput pulse at terminal "20, as illustrated in curves 35 and 3.6. Whenthe reverse switching process occurs at time t7, diode .25 conducts andrestores, across capacitor 23, a reference voltage whose magnitude isdependent upon the setting of potentiometer 21. The length of time, orthe number of pulses or steps, required to initiate the reverseswitching process in the multivibrator is dependent upon both thesetting of potentiometer 21, which determines the reference negativebias at grid 16 of device '5, and upon the setting of potentiometer l3,which determines the anode current of device 4 and, therefore, themagnitude of the negative pulse supplied to grid 16 of device 5 at theinitiation of a switching process. In practice, either potentiometer 2!or potentiometer I3 is permanently set, and the other is varied todetermine the length or timeduration of the rectangular output pulse.

In operation, the time-duration of the rectangular output pulse isalways an exact multiple of the time between trigger pulses. With thecircuit of my invention, the count or number of periods comprised Withinthe time-duration of the rectangular pulses is definitely fixed. Theoperation remains stable because the number of trigger pulse periodscontained within one rectangular output pulse is determined largely bythe voltage divider action of potentiometer 53 which remains constantregardless of temperature drift. With my invention, the tendency of theswitching process to shift in occurrence between adjacent pulses fromthe timing circuit is largely eliminated.

While a certain specific embodiment has been shown and described, itwill, of course, be understood that various modifications may be madewithout departing from the invention. The appended claims are thereforeintended to cover 6. any suchimodificationsiwithin the truespiritsandscope of the invention.

7 What I claimas new and desire to secure by Letters Patent of theUnited States is:

1. A system for generating a voltage pulse of predeterminedtime-duration after an initiating impulse, comprising a multivibrator,said multivibrator comprising time constant-circuits providing saidmultivibrator with one condition of stability, means for applyingsaidimpulse to said multivibrator to. disturb said condition ofstability, means responsive to said impulse for generating a series oftriggering pulses at predetermined time intervalsafter saidoccurrence, aunilateral charging circuit comprising said multivibrator time constantcircuits responsive tosaid triggering pulses for generating astepvoltage which increases by one step at a time for each ofsaidtriggering pulses, said multivibrator being responsive to apredetermined level of said step voltage for returning to said conditionof stability.

2. A system for initiating an increment of voltage upon the occurrenceof successive electrical impulses and for terminating said incrementafter a fixed number ofequal time intervals beginning with saidoccurrences, comprising a multivibrator, said multivibrator comprisingtime constant circuits providing said multivibrator with one conditionof stability, means for applying said impulses to said multivibrator todisturb said condition of stability and to cause an increment of voltagein said multivibrator upon the occurrence of said impulses,said voltageincrement maintaining said multivibrator in said disturbed condition fora given interval, means responsive to said impulses for'generating aseries of triggering pulses at predetermined relatively shorttime-intervals after said occurrences, a unilateral charging circuitcomprising said multivibrator time constant circuits responsive to saidtriggering pulses forgenerating a step voltage by the accumulation of a'definiteamount of charge in response to each one of said triggeringimpulses, said multivibrator responsive to a predetermined level of saidstep voltage for returning to said condition of stability and toterminate said increment before the expiration of said given interval.

3. A system for initiating an increment of voltage upon the occurrenceof successive electrical impulses and for terminating said incrementafter a fixed number of equal time intervals beginning with saidoccurrences, comprising a multivibrator, said multivibrator comprisingtime constant circuits providing said multivibrator with one conditionof stability, means for applying said impulses to said multivibrator todisturb said condition of stability and cause an increment of voltage insaid multivibrator upon the occurrence of said impulses, said voltageincrement maintaining said multivibrator in said disturbed condition fora given time interval, a trigger circuit responsive to each of saidimpulses for generating, a series of triggering pulses at time-intervalssubstantially less than said given interval, said trigger circuit havingan output terminal connected in series with an impedance and a rectifierto said multivibrator, time constant circuits, said impedance rectifierand time constant circuits forming a storage circuit to produce a stepvoltage increasing by a small increment in response to each of saidtriggering pulses, and said multivibrator responsive to a predeterminedlevel of said step voltage for returning to said condition of stability,thereby terminating said increment of voltage.

4. A pulse generating system comprising a source of initiating impulses,a pair of electron discharge devices each having an anode, a cathode anda control electrode, a common resistive connection from both saidcathodes to a common point of fixed potential, separate resistiveconnections from said anodes to a point of positive potential withrespect to said fixed potential, a voltage bias source, means to applysaid bias to the control electrode of one of said devices to maintainsaid one device normally non-conducting, a capacitive connection fromthe anode of said one device to the control electrode of said otherdevice, a connection from said impulse source to the control electrodeof said one device to render said one device conducting and said otherdevice non-conducting upon the occurrence of an initiating impulse, atrigger circuit connected to said source for generating, in synchronismwith the occurrence of an initiating impulse, a series of triggeringpulses at time intervals substantially less than the intervals betweensaid initiating impulses, said trigger circuit having an output terminalconnected in series with an impedance and a rectifier to the controlelectrode of said other device, said rectifier poled to produce at saidcontrol electrode a step voltage increasing by a small increment inresponse to the positive going portion of each of said triggeringpulses, a second rectifier biased to a negative potential with respectto said fixed potential, said second rectifier connected to the junctionof said first rectifier and impedance and poled to be conductive inresponse to the negative going portion of each triggering pulse, saidstep voltage being of a polarity to render said other device conductingafter the attainment of a predetermined magnitude by step voltage.

5. A pulse generating system comprising a source of initiating impulses,a pair of electron discharge devices each having an anode, a cathode anda control electrode, a common resistive connection from both saidcathodes to a common point of reference potential, separate resistiveconnections from said anodes to a point of positive potential withrespect to said reference potential, a voltage bias source, means toapply said bias to the control electrode of one of said devices tomaintain said one device normally conducting, a capacitive connectionfrom the anode of said one device to the control electrode of said otherdevice, a connection from said impulse source to the control electrodeof said one device to render 1 said one device conducting and said otherdevice non-conducting upon the occurrence of an initiating impulse, atrigger circuit connected to said source for generating, in synchronismwith the occurrence of an initiating impulse, a series of triggeringpulses at time intervals substantially less than the intervals betweensaid initiating impulses, said trigger circuit having an output terminalconnected in series with an impedance and a first rectifier to thecontrol electrode of said other device to produce thereat a step voltageincreasing by a small amount in response to each of said triggeringpulses, said first rectifier being poled to conduct on a positive goingvoltage, a second rectifier connected between the junction of said firstrectifier with said impedance and a point of negative potential withrespect to said reference potential, said second rectifier being poledto conduct on a negative going voltage.

ROBERT E. MOE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,405,237 Ruhlig Aug. 6, 19462,411,648 Brauer Nov. 26, 1946 2,420,516 Bischofi May 13, 1947 2,430,547Anderson Nov. 11, 1947 2,444,036 Crost June 29, 1948

